Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes
Miroslav Lichvar <mlichvar@redhat.com> Tue, 05 March 2019 13:00 UTC
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Date: Tue, 05 Mar 2019 14:00:03 +0100
From: Miroslav Lichvar <mlichvar@redhat.com>
To: Daniel Franke <dfoxfranke@gmail.com>
Cc: ntp@ietf.org
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Subject: Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes
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I have some data with respect to the concern that existing clients may be unintentionally sending requests in the interleaved mode and not being able to process the responses. There was a discussion about this on the last interim meeting, but some people who I think would be interested and may had useful comments were not present, so I'm repeating it here. I have analyzed NTP traffic on three public servers from the pool.ntp.org project, in three different countries (all included also in the global zone). They were capturing the traffic for about two weeks. In total it was about 3.5 billion requests. I've excluded my own clients and testing tools using the interleaved mode from the analysis. About 20% of all requests had a non-zero origin timestamp. About 0.0002% of all requests were in the interleaved mode (receive timestamp different from transmit timestamp and origin timestamp equal to one of the server's previous 50 million receive timestamps). All clients that sent an interleaved request seemed to use the mode consistently. There was not a single interleaved request generated by chance. There were two clients sending interleaved requests, but not able to process an interleaved response, i.e. it was always followed by a request using the origin timestamp from the last basic response. Both clients were identified as the older NTPsec version which had an incompletely removed implementation of the interleaved mode. So, it doesn't look like there is a client that accidentally implemented requests in the interleaved mode on its own, e.g. by not strictly following the existing RFCs. The question is what, if anything, should be done about clients that have or will have an incomplete or buggy implementation of the interleaved mode. That could happen at any time and it doesn't matter how the protocol is designed, if it's using an extension field, or not. One option is to change the draft to require the servers to drop the pair of receive and transmit timestamps once it has been used to generate a response. That will force the protocol to fall back to the basic mode when the client is not able to process the response. In the worst case this would effectively cause a 50% packet loss, but the client would still be able to synchronize to the basic responses. The drawback is that the protocol will fall back to the basic mode when the response is really lost, when the server could still have responded with the same timestamp to the following request and the client was able to process it. Thoughts? -- Miroslav Lichvar
- [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Karen O'Donoghue
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Tal Mizrahi
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Miroslav Lichvar
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Karen O'Donoghue
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Salz, Rich
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Denis Reilly
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Harlan Stenn
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Miroslav Lichvar
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Harlan Stenn
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Miroslav Lichvar
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Harlan Stenn
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Daniel Franke
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Miroslav Lichvar
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Miroslav Lichvar
- Re: [Ntp] WGLC: draft-ietf-ntp-interleaved-modes Miroslav Lichvar